1. Field of the Invention
The present invention is directed to a traffic signal lamp, and in particular to a variable message traffic signal (hereinafter, referred to as "VMTS") lamp capable of displaying various signal lights or messages in accordance with predetermined signal plans.
2. Description of the Background Art
Traffic signal lights composed of a plurality of lamps each having a single color or symbol are generally installed at intersection approaches in order to control the flow of automobiles and pedestrians therethrough.
A conventional traffic signal light includes several lamps, each lamp adopted in a casing equipped with an electric bulb and a color lens at the front side thereof, the color lens being red, green, amber or showing other symbols in accordance with traffic signal messages to be displayed.
Traffic signal lights are displayed in a number of fashions. Firstly, the traffic signal lights are divided into automobile use and pedestrian use. The former is operated basically by green and red lamps to show a green phase meaning proceed, and a red phase meaning stop, and may be supplemented by an amber lamp to warn of the change of a green phase into a red phase. The green phase may be supplemented with a leading left-turn phase or a lagging left-turn phase to specify left-turn provision. In order to display the leading or lagging left-turn phases an additional lamp showing an arrow pointing to the left side is adopted to the traffic signal head. It is also possible to have a combined phase to allow straight-through and left-turn traffic at the same time. This synchronous phase can be displayed by lighting up the green lamp and the left-turn arrow lamp simultaneously, or alternatively, using a specially designed two-leg arrow with legs pointing respectively forward and leftward.
Alternatively, as in Ontario, Canada, for example, the synchronous phase is displayed by flashing the green lamp.
The latter, a pedestrian traffic signal light, is operated simply by a green lamp meaning proceed and a red lamp meaning stop, without any warning amber lamp. The green and red lamps may be substituted by words such as "walk", and "stop" or even by symbols such as a man walking, or a palm to indicate don't walk. Lastly, there is also a variable traffic lane signal lamp capable of showing a green arrow pointing downward or a red "X".
Furthermore, the green, red and amber lamps can be used in a flashing fashion. For example, a flashing single amber lamp may be adopted at locations where drivers' attention to safety is required.
As explained above, a traffic signal head may contain up to four lamps of various colors, symbols or even characters. These numerous fashions of signal lamps require numerous design standards and regulations thus raising complexity in traffic signal design and operations. Also, a traffic signal head may become structurally huge and heavy, thereby resulting in high fabrication and installation cost. Furthermore, the big size and the weight of the traffic signal head require a strong supporting structure to be able to resist against the wind force.
The conventional traffic signal lamps for automobiles are arranged vertically or horizontally. However, the lamps for pedestrians are usually arranged in a vertical direction.
The red light is displayed at the top in the case of a vertical arrangement, and at the far left in the case of a horizontal arrangement, and the green light is displayed at the bottom and far right in the respective cases, and thus one can distinguish signal messages by the position thereof. That is, when a signal lamp is turned on and illuminating, then even one with color blindness or impaired color vision can distinguish the signal messages by the positions of the lighted and extinguished signal lamps.
Today's traffic signal lights are displayed by lighting up an electric bulb of a lamp or lamps selected from the set of lamps as mentioned above. The selection of appropriate lamp(s) is made through a signal phase plan, which designates the sequence and the duration of such signal phases as green, amber and red for each signal head installed at each approach of an intersection. Traffic situations can vary by the time of a day and each such traffic situation require a specific signal phase plan. For example, in the morning rush hour, a different signal phase plan is required from the evening rush hour or off-peak hours. In order to select an appropriate phase plan at the right time, and operate the selected plan by switching on or off the signal lamps, an instrument called, a traffic signal controller, housed in a weather-proof case is installed normally on the ground separated from the signal head.
This conventional signal system comprising numerous electric lamps and an electromechanical switching mechanism consumes a substantial amount of electric power compared with modern electronic technologies, and requires frequent replacement of bulbs and parts, and careful maintenance. All these outdated technologies result in high total cost and environmental burden.
Despite the complex structure of the traffic signal head, the conventional traffic signal lights convey only simple messages such as to proceed, turn left, or stop. This is because each lamp can display only one message when it is lighted.